Mountaineer Ali Sadpara, the only person to have scaled the peak in winter, said he saw a three-person tent "invaded by snow" while on board a Pakistani army helicopter. However, it is not known if the tent belonged to the missing climbers.

Mr Sadpara has also told the AFP news agency that heavy snowfall and the risk of avalanche has made a ground search "almost impossible".

Image caption
Alison Hargreaves died while descending from the summit of K2 in 1995